Atomistic View of Laser Fragmentation of Gold Nanoparticles in a Liquid Environment

Abstract

Short-pulse laser irradiation of a colloidal solution of nanoparticles is an effective method for fragmenting the nanoparticles and producing a population of smaller nanoparticles and atomic clusters with properties desired in various fields of applications, including biology, medicine, and catalysis. To investigate the mechanisms involved in the fragmentation, we develop a computational model capable of realistic treatment of a variety of interrelated processes occurring on different time and length scales, from the electronic excitation by the laser pulse, to the electron–phonon energy transfer and an explosive phase decomposition of the superheated nanoparticle, and to the generation and collapse of a nanobubble in a liquid environment. The application of the model to simulation of laser fragmentation of a Au nanoparticle in water has revealed two distinct channels of the formation of the fragmentation products. The first channel involves the direct injection of compact nanodroplets propelled by the phase explosion of the irradiated nanoparticle deep into the water environment. The second channel of the nanoparticle formation involves a more gradual growth through agglomeration of numerous atomic clusters embedded into a narrow region of water surrounding the laser-induced nanobubble. This channel produces irregularly shaped nanoparticles and leads to a rapid decline of the population of atomic clusters on the timescale of nanoseconds. All the clusters and nanoparticles experience an ultrafast quenching by the water environment and feature a high density of twin boundaries and other crystal defects, which may enhance the density of active sites for the catalytic applications of the nanoparticles. The computational predictions of the prompt generation of a high concentration of the fragmentation products in a relatively narrow shell-like region on the outer side of the nanobubble, as well as the rapid solidification of atomic clusters and nanoparticles at the early stage of the nanobubble formation, have important practical implications for the design of new methods aimed at achieving an improved control over the size, shape, and defect structures of nanoparticles produced by laser fragmentation in liquids.

Engineering of Cation Occupancy of CoFe2O4 Oxidation Catalysts by Nanosecond, Single‐Pulse Laser Excitation in Water

“…[33] Note, that in the case of laser post-processing with fs-, ps-, and ns-pulsed lasers in water, the cooling of the nanoparticles from several hundreds and even thousands of Kelvin down to ambient temperature occurs on the time scale of only a few 100 ns [38] after excitation, which leads to many orders of magnitude higher cooling rates in the range of 10 10 K/s. [34] On the other hand, the effective temperature reached during heating by the nanosecond laser pulse increases with the laser pulse intensity. From the degree of inversion reached for the wet-chemical and commercial samples at the highest laser intensity of 1 • 10 12 W m À 2 , an effective temperature around 900 °C can be expected from the comparison to Ref.…”

“…[22,23,35,36] After laser heating induced by the pico-or nanosecond laser pulse, the particles rapidly cool down to ambient temperature within ~100 ns (~10 10 K s À 1 ) due to heat transfer from the nanoparticle to the liquid. [34,37,38] Earlier studies on pulsed laser fragmentation have also shown that the size reduction is very often accompanied by a superimposed alteration of the crystal defect density [6,24] and the formation of mixed crystal phases. [25,26] During fragmentation of Co 3 O 4 , [5] CoFe 2 O 4 [25] , and BiFe 2 O 4 [26] , Waag et al observed the occurrence of rocksalt-type CoO, [5] layered double hydroxides, [25] and carbonate impurities.…”

Influence of Pt Alloying on the Fluorescence of Fully Inorganic, Colloidal Gold Nanoclusters

“…The defects of AuPt NCs may originate from or could be further intensified by the LFL synthesis process. Re-irradiation of larger NPs initiates a phase explosion, [24,37] followed by sudden cooling of the fragmentation plume, [24] causing the spontaneous solidification in the thermodynamically unfavoured distorted (3 j 1 j 1) surface lattice structure. [21] It has been reported that laser-generated NPs are often defect-rich, caused by cooling rate of 10 12 -10 13 K/s during this kinetically-controlled synthesis.…”

“…[21] It has been reported that laser-generated NPs are often defect-rich, caused by cooling rate of 10 12 -10 13 K/s during this kinetically-controlled synthesis. [31] Recently, Zhigilei et al reported that NCs are ejected directly into the dense cold water during LFL, [37] indicating even faster cooling-rates. The distortion depends on the cooling rate, atomic radius, and materialdependent properties.…”

“…Recently, Zhigilei et al. reported that NCs are ejected directly into the dense cold water during LFL, [37] indicating even faster cooling‐rates. The distortion depends on the cooling rate, atomic radius, and material‐dependent properties.…”